Whatever he designed, and however long he stayed, Italo Zucchelli was going down in the history books at Calvin Klein—likewise Francisco Costa, his womenswear counterpart—because they were the first designers to helm the Klein label bar “Calvin Clean” himself, handpicked by the house founder and given the reins upon his retirement in 2003.

Costa offered a seductive, engineered vision of femininity that pushed well beyond the confines of strict ’90s minimalism—beyond the spaghetti-strapped slip dress and white T-shirt and Kate Moss in the Obsession adverts that instantly leap to mind, even today, with the mention of Klein’s name. He created intricately worked garments that appealed, subtly, to shifting tastes in sexuality and decoration and the rise in demand for clothes that defined luxury in fabric and construction; in short, he moved with the time. But, for me, it was the Klein forged by Italo Zucchelli that proved most potent and emphatic.

Maybe that’s because Klein’s breed of masculinity has always been eye-popping—like the 1982 Bruce Weber shots of pole-vaulter Tom Hintnaus, shot from below like a Greek god (appropriate, for an Olympic athlete) clad only in his Calvin Klein underwear. It was man as sex object, in a postfeminist, post-gay liberation world—and Klein claimed him as his own. Klein’s vision was so intrinsically tied with male sexuality that, when the designer launched a complementary line for women in 1984, it was based on the men’s, with vestigial fly-front still intact.

Italo Zucchelli’s first recollection of Klein was that billboard, as a teenager (he was born in 1965) growing up in La Spezia in northwest Italy. “You had a man, in his underwear, on a billboard in 1982 . . . Now it’s everywhere. We’re used to it, we don’t think about it. But then . . . it was the first time. There is always this element, of the masculinity, of the sexuality, expressed in different ways. It’s part of the language of Calvin Klein.”

Zucchelli’s Calvin Klein is notable—and will always be memorable—for the way he played with that same sense of masculinity and sexuality. It wound up looking unlike anything else in fashion—certainly unlike anything else in Milan. One season we had Übermensch Starship Trooper types in abbreviated bombers and peaked baseball caps; another, anatomically re-engineered, flesh-colored performance sports gear, as if the models were clad, Silence of the Lambs style, in suits made of skin. These were man suits (albeit not made of real men), transforming the skinny kids Zucchelli cast each season into godlike Klein boys. He actually did that every season, with clothes tailored subtly but distinctly to transmogrify a man’s body into something better.

Zucchelli’s final men’s collection for Fall was inspired, in part, by the Anne Hollander book Sex and Suits, where Hollander makes a compelling argument for suits as the ultimate expression of male power, and eroticism. Could there be anything more Calvin Klein than that? Hence the fact Zucchelli brought his tailoring skills to the fore to re-engineer not just fabric, but the body of his men (and, for the first time, women). That’s why Klein always stood out: The men looked different. Bigger, butcher, beefier, but never a himbo. Zucchelli invariably described it as “American”—which he has an oddly developed understanding of, given that he’s an Italian. He once told me, with a smile, “We are all Americanized!”

Designers who inherit labels from house founders are often tasked with establishing “codes,” those hallmarks and decorative devices design labels are obsessed with nailing to ensure their continuance in perpetuity (and, indeed, in absentia). But Klein’s codes were already well established, and world famous—Klein’s advertising was seen farther and probably packed more of a punch than his clothing ever did. So Zucchelli was allowed to play with the codes of Calvin, to experiment and even reinvent them. That’s why we ended up with the Klein denim reworked as a precious, intricate trompe l’oeil jacquard; his fragrance names—Obsession and Eternity—in relief on bubbly neoprene sweatshirts; or the signature logoed underwear waistband attached to skinny stretch suit pants.

Just as the Calvin Klein Collection models were transformed by their clothes, so Zucchelli’s best work transformed ordinary, even humble clothing into fashion, without alienating the wearer. “That’s what I think my job is,” he said to me, after his last show of slick, sexy suits mixed with more of that haute couture denim look-alike stuff, a technological marvel that’s quintessentially Zucchelli. “I like the high and low. That’s how we dress. That’s modern.” Ultimately, that’s his legacy: He made Calvin Clean, the menswear master of the ’90s, into a designer relevant to an entire new generation.